In the previous millennium, mediatheques were merely libraries with shelves full of books. Finding a book in a library was not always an easy task to do, but was nevertheless facilitated by it being distinguished according to various formats, colors, sizes and materials. So discriminating between a cook book, a dictionary, a comic book, an atlas, a schoolbook, a picture book, a prayer book, a cashbook, an account book, was not so difficult. With the recent explosion of electronic media, it is today quite common to find all these different books recorded on a common media following worldwide standards in terms of physical form factor, size and even colors. Either CD's or DVD's can record any type of information, not only text and images as books did, but also sound and video. The result is that state of the art mediatheques are now with shelves full of objects that follow or not the same format. Finding a given object within such a mediatheque becomes much more demanding as it was in the past.
To overcome this difficulty, the RFID technology provides an interesting capability allowing to uniquely identify an RFID tag, and subsequently the object it is attached to. For example, U.S. Pat. No. 6,693,539 discloses an article inventory control system for articles, such as books, using Radio Frequency Identifier (RFID) tags attached to the articles. Each tag has a unique identification or serial number for identifying the individual article. An inventory database tracks all of the tagged articles and maintains circulation status information for each article. Articles are checked out of the library using a patron self-checkout system. Checked out articles are returned to the library via patron self-check in devices. The shelves are periodically scanned with a mobile RFID scanner for updating inventory status.
The current RFID technology allows to assign a unique identifier to an RFID tag, so that this tag can be uniquely identified when read by an RFID reader. Establishing a one-to-one relationship between the RFID tag and the object it is attached to, allows consequently to uniquely identify a given object among a set of objects. Thus, an obvious solution for localizing objects in shelves consists in sticking an RFID tag onto each object, to associate each object with the attached RFID tag, and then to read the RFID tag identifier by implementing an RFID reader. To make such a solution affordable, the RFID tags have to be inexpensive, robust and thin, so that only passive RFID tags are considered. This limitation brings a cumbersome constraint as the reading range of passive RFID tags is quite limited, typically few inches. In order to locate a given object within a set of shelves, the reader will have to pass close to each shelf, scanning all of its width. This either asks for a tedious and precise manual operation, or to put in place an expensive robot. Active RFID tags do not suffer from this short reading range, but are unfortunately not well suited, due to their price and more important due to the fact that they have to include a power source (like a battery) bringing stringent form factor constraints.
Therefore, there is a need for innovative RFID tags allowing long reading range while being equivalent in terms of size, form factor, and price to the passive RFID tags, for identifying objects in mediatheques, libraries, book-stores, or any place where objects (e.g., books, CDs, DVDs, etc) may be stored in a stackable arrangement.